Director General Ahmet Uzumcu of the Organisation for the Prohibition of Chemical Weapons, OPCW, gives an update on the chemical watchdog’s verification and destruction mission in Syria during a press conference in The Hague, Netherlands, Wednesday.

THE HAGUE, Netherlands — International inspection teams overseeing the destruction of Syria’s chemical weapons will have to negotiate cease-fires between government and rebel forces to gain access to some sites, officials closely involved with the mission said Wednesday.

The revelation is a clear indication of the risks and difficulties of the unprecedented disarmament plan, and it suggests that the effort to rid Damascus of its poison gas stockpile may have a hard time meeting its mid-2014 deadline.

The destruction of the stockpile is being led by a joint team from the United Nations and the Organization for the Prohibition of Chemical Weapons.

OPCW Director-General Ahmet Uzumcu told reporters in The Hague the timeline was tight but “not unrealistic.” He said inspectors have to visit more than 20 sites in coming days and weeks. Since the mission started last week, they have been to one location; they are expected to inspect a second site near Damascus, the Syrian capital, on Wednesday.

This is the first time the global organization that polices the Chemical Weapons Convention has sent its inspectors and analytical chemists into a raging civil war, and their security is a major concern amid ongoing fighting between President Bashar Assad’s forces and various rebel groups. The war has already left at least 100,000 people dead.

On Wednesday, rebels overran a military post near the southern city of Daraa, according to the Britain-based Syrian Observatory for Human Rights activist group. Opposition fighters late last month also captured a nearby military base that previously served as the customs office on the outskirts of Daraa.

“If we can ensure some cooperation by all parties and if some temporary cease-fires ... can be established in order to permit our experts to work in a very hostile environment, I think the targets could be reached,” Uzumcu said in his first public remarks on the mission.

Previous attempts by international mediators to negotiate broader cease-fires have failed, though it might be easier for combatants to agree to halt their fire in a specific location for a limited time.

Two large umbrella groups for the Arab and Muslim world — the Arab League and the Organization of Islamic Cooperation — are urging those fighting in Syria to halt fighting for the duration of next week’s four-day Muslim holiday of Eid al-Adha, the Arab League’s deputy secretary general, Ahmed Ben Heli, told reporters in Cairo on Wednesday.

At The Hague, another senior OPCW official, Malik Ellahi, said that while cease-fires will be vital for some locations, Damascus has consolidated many of its weapons into secure locations away from rebel-held territory.

“So far what we have been told is that most of the sites and facilities that we need to inspect are in government control,” he said.

Even so, the teams of inspectors will need security clearances wherever and whenever they move. An inspection team “will only go and conduct its mission ... if it is assured that security on a given day, on a given schedule is provided,” Ellahi said.

Uzumcu said Syrian authorities’ dealings with inspectors have so far been constructive and cooperative.

The officials said it is too early in the mission to speculate on exactly how and where chemical weapons will be destroyed and how many inspectors will be needed.

The OPCW has already said it will likely need to hire more staff to cope. U.N. Secretary-General Ban Ki-moon has estimated that the joint U.N.-OPCW mission will likely number around 100 staff.

On Wednesday, a new team of inspectors arrived in a convoy of six U.N. cars at a hotel in Damascus, a witness said. OPCW officials have said a dozen new inspectors were expected Wednesday, joining an initial team that has been in Syria since last week.

Experts say the weapons and precursor chemicals that are mixed to make poison gas and nerve agents like sarin can be either chemically neutralized or incinerated.

OPCW spokesman Michael Luhan said that despite the risky nature of the disarmament program, there were “no shortage of sign-ups” among the organization’s inspectors to take part in what is a voluntary mission.

In other developments Wednesday, two mortar shells from Syria struck an Israeli military post on the Golan Heights, lightly wounding an Israeli soldier.

Israel’s military said it struck back, hitting the source of fire, but did not specify if the mortars came from a rebel or government position.

Gunfire and mortar shells from Syria periodically land in the Israeli-controlled Golan. Israel believes most of the fire, including Wednesday’s, is errant spillover from the Syrian civil war. But in some cases, it has accused Syrian forces of intentionally firing into the Golan.

In France, Prime Minister Jean-Marc Ayrault revealed, apparently by mistake, that two more journalists were being held hostage in Syria.

The French Foreign Ministry said the kidnapping of Nicolas Henin and Pierre Torres had not been disclosed until now, in line with their families’ wishes.

However, in an interview on French radio station Europe 1, Ayrault named them for the first time while answering a question about two other reporters kidnapped in June.

Press freedom advocate Reporters Without Borders said 25 reporters have been killed and 32 imprisoned since the start of Syria’s conflict in March 2011.